Electronic device and method of making

ABSTRACT

Disclosed is an electronic device comprising a glass, glass ceramic, or ceramic sheet having a thickness less than about 0.4 mm and wherein a minimum strength of the inorganic substrate is greater than about 500 MPa. Also disclosed is a method of making an electronic device including drawing a viscous inorganic material to form an inorganic ribbon having opposing as-formed edges along a length of the ribbon, separating the ribbon to form a substrate sheet of inorganic material comprising two as-formed edges and forming a device element on the inorganic substrate.

This application claims the benefit of priority under 35 U.S.C. § 119(e)of U.S. Provisional Application Ser. No. 60/849,298 filed on Oct. 4,2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to the manufacture of electronicdevices, and in particular electronic devices formed using one or morethin flexible sheets of an inorganic material.

2. Description of Related Art

Display devices utilizing plasma, liquid crystal, or organic lightemitting diode display elements, to name a few, are fast overcomingcathode ray tube (CRT) displays in commercial products, finding use in amyriad of applications, from cell phones to televisions. However, theintroduction of very thin, light weight, or flexible displays is only inits infancy. This is due in no small part to the tremendous structuraldemands placed on such display devices: they must be capable ofwithstanding repeated flexing or bending or other stress without harm tothe device or the substrate on which it is disposed; due to the intendeduse of thin, light, or flexible displays in portable devices, they areexpected to withstand rough handling, again without undue harm to thedevice or substrate, and; they must be capable of withstanding impact ora bending radius that can be less than 2 cm, and less than 1 cm in somecases.

One material contemplated for use in thin, light weight, or flexibledisplays or electronic devices is glass. Glass is generally chemicallyresistant, transparent, can form a hermetic barrier or seal, cantolerate typical electronic fabrication temperatures, and may be formedinto very thin sheets. Sheets in excess of 10 m² having thicknesses lessthan 1 mm, and even less than 0.7 mm have been produced and routinelyused, and glass sheets are soon expected to reach dimension of at leastabout 100 m². In a typical display manufacturing process, multipledisplays are formed using one or more large glass sheets or substrates.The displays are then separated into individual display units, usuallyby scoring and breaking or other cutting methods. Thus, very large glasssheets are efficiently utilized by producing as many display orelectronic units as possible.

Cutting glass, and in this case glass sheets, generally forms flaws(e.g. cracks) in the edges of the glass sheets. These flaws can serve ascrack initiation sites, and thereby reduce the strength of the sheets,particularly if the glass is flexed such that the flaw experiencestensile stress. Generally, typical display devices do not experiencesignificant flexing, thus the existence of these flaws is not ofsignificant concern: Typical cutting methods produce edges of sufficientstrength to survive both the standard device processing conditions andcurrent application end use.

Shown in FIG. 1 is a Weibull plot showing the failure probability for 75micron thick glass sheets in four-point bending according tostandardized four-point bending tests (e.g. ASTM). The samples in thiscase were 5 mm wide×30 mm long×75 microns thick. The samples were testedin a four-point bend arrangement standing on edge so the tensile stresswas applied across the entire 75 um face thickness. The glass sheetrepresented by curves 10 and 12 were laser cut, while the glass sheetrepresented by curve 14 was mechanically scribed and separated bybending to fracture the sheet. As depicted, none of the samplesrepresented by the curves showed a high probability of withstanding astress in excess of about 300 MPa. The samples for mechanical scoring,the most widespread method of separating glass, did not show a highprobability of withstanding a stress in excess of 100 MPa. Althoughstandard cutting methods for glass substrates greater than 0.4 mm thickaddress the needs of current device manufacturing processes orapplication end use, higher edge strength is required for substratesless than 0.4 mm thick as may be used in emerging processes andapplications such as flexible displays.

Flexible displays or flexible electronic devices, by the very nature oftheir flexibility, may produce significant stress in the display orelectronic substrate(s), either during the manufacturing process or inuse. Thus, flaws that might be present in the glass may experiencestresses sufficiently great that the glass will crack, causing the glassto fail. Since typical display manufacturing involves cutting the glassto form individual displays, and cutting is known to create multipleflaws in the glass along the cut edge, this bodes poorly for the fate ofglass substrate-based flexible display devices.

Attempts to mitigate flaws at the edges of glass sheets have includedlaser cutting, grinding, polishing and so forth, all in the attempt toremove or minimize the flaws that are created when the glass sheet iscut to size. However, many of these approaches are unsatisfactory forflexible electronic applications, either because the technique isincapable of removing flaws down to the size needed for the expectedstresses, or the technique is difficult to apply to such thin glasssheets (less than about 0.4 mm thick) in a manufacturable process orscale. Acid etching of the glass edges may be used, but acid etching mayalso degrade the display or electronic device disposed on the substrate.

BRIEF SUMMARY OF THE INVENTION

In one embodiment of the present invention a method of making a displayor electronic device is disclosed comprising providing a ribbon ofinorganic material having opposing as-formed edges along a length of theribbon, forming an electronic element on the ribbon, and separating theribbon of inorganic material to form a sheet of inorganic materialhaving opposed as-formed edges and an electronic element disposedthereon.

In another embodiment, an electronic device is described comprising asheet of inorganic material comprising a thickness less than about 0.4mm and at least two as-formed edges and at least one layer of anelectroluminescent, semi-conducting or conducting material disposed overthe glass sheet.

In still another embodiment, an electronic device is disclosedcomprising a substrate comprising a glass sheet formed by a downdrawprocess, the glass sheet having a thickness less than about 0.4 mm andat least two as-formed edges in an opposed relationship, and anelectrically active material disposed over the glass sheet.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary of theinvention, and are intended to provide an overview or framework forunderstanding the nature and character of the invention as it isclaimed.

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings are not necessarily to scale,and sizes of various elements may be distorted for clarity. The drawingsillustrate one or more embodiment(s) of the invention, and together withthe description serve to explain the principles and operation of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of failure stress probability for glass samplesseparated (cut) by both mechanical scoring and laser cutting.

FIG. 2 is a front view of a portion of a downdraw glass sheetmanufacturing process showing how individual glass sheets are typicallycut from the drawn ribbon of glass.

FIG. 3 is a top view of an intermediate display manufacture showingdisplay elements arranged on a glass sheet or substrate before theindividual devices are separated from the parent sheet.

FIG. 4 is a front view of a portion of a downdraw glass sheetmanufacturing process showing how individual glass sheets are typicallycut from the drawn ribbon of glass in accordance with an embodiment ofthe present invention.

FIG. 5 is a perspective view of a display or electronic device formed inaccordance with an embodiment of the present invention.

FIG. 6 is a perspective view of a bending mode for a display orelectronic device made in accordance with an embodiment of the presentinvention.

FIG. 7 is a perspective view of another bending mode for a display orelectronic device made in accordance with an embodiment of the presentinvention.

FIG. 8 is a cross sectional view showing how a ridge is formed at anedge of a glass ribbon in accordance with an embodiment of the presentinvention.

FIG. 9 is a cross sectional view of a glass sheet bent into a “U” shapeand illustrating the location of the tensile, neutral and compressivestress regions.

FIG. 10 is a cross sectional view of a display or electronic device inaccordance with an embodiment of the present invention showing ridges inthe neutral plane of as-drawn edges.

FIG. 11 is a plot of the minimum bend radius at failure for multiplesamples of two different types of glass sheets, showing the superiorperformance of the samples having as-drawn edges.

DETAILED DESCRIPTION

A conventional downdraw process for forming glass sheets may be, forexample, a slot draw process, an overflow process, a fusion process or aredraw process. In a slot draw process, a molten raw material is drawnfrom a slot in the bottom of vessel containing the molten material. Thedimensions of the resulting glass sheet are determined in part by thesize and shape of the slot, the temperature/viscosity of the molten rawmaterial, and the draw speed.

In a one-sided overflow process, the molten raw material is flowed overthe upper edges of a long vessel or pipe. The finished glass sheetincludes one side that has been in contact with the vessel, while theother side is relatively pristine, having not contacted the vessel sidesduring the overflowing.

In a variation of the overflow process, a molten raw material is flowedover both sides of a vessel or pipe having inclined sides that convergealong the bottom of the vessel. The two separate flows rejoin along theline of convergence between the sides to form a single sheet which coolsinto a glass ribbon. The ribbon may thereafter be cut into smallersheets.

Advantageously, the raw material from both streams of raw material thatflow over and is in contact with the converging forming surfaces isjoined in the center of the glass sheet, while the pristine surface ofeach flow becomes the outside surfaces of the glass sheet, providing aglass sheet of exceptional quality and clarity, making this so-called“fusion” process an ideal source of display glass.

For the purposes of simplicity, and not limitation, the followingdescription is presented in terms of a re-draw process, with theunderstanding that the present invention is applicable to other methodsof forming glass sheet less than 0.4 mm in thickness.

In a conventional re-draw process, a previously formed glass (i.e. apreform) is reheated above the softening point of the glass andstretched longitudinally (length-wise) and/or transversely (width-wise)to form a glass ribbon. The thickness of the ribbon and the width of theribbon are dependent, inter alia, on the shape of the preform, thepulling force applied to the ribbon, and the viscosity of the glass. Thepreform may be, for example, a previously formed glass sheet made by anyof the preceding processes, or any other process capable of producing aglass preform of the appropriate size and shape, such as a float processor soot consolidation process. Typically, the glass ribbon is drawnvertically downward, during which time the glass attenuates, both inthickness and width—the ribbon becomes thinner and narrower. The edgesof the ribbon may be guided, or pulled with suitable rollers, but mayalso be untouched, with the pulling, or drawing force originating fromthe bottom of the glass sheet only. The as-drawn or as-formed edges aregenerally rounded due to surface tension at the still viscous edges, butmay take other shapes, such as tapered or rectangular, depending on theprocess type and process parameters. For example, in a slot drawprocess, the shape of the slot and the viscosity of the glass may bevaried to produce a generally tapered edge or more rectangular edge.

The strength of glass is dictated by the presence of flaws in the glass.If tensile stress is applied to glass having a flaw, the stress becomesconcentrated at the flaw. A flaw may be a microscopic crack for example,in which case the stress is concentrated at the tip of the crack. If thestress exceeds a certain magnitude, the original flaw—the crack—maygrow. If sufficient stress is applied, crack growth may be virtuallyinstantaneous, leading to catastrophic failure of the glass: it breaks.

Analogous to the strength of a chain being based on the strength of theweakest link, the strength of glass may be characterized as the strengthof the largest, and therefore weakest, flaw. For example, if a tensilestress of 10 kpsi (70 MPa) is applied to a glass fiber, and the fiberholds firm, the fiber is said to have a strength of at least 10 kpsi.That is, all the flaws that may exist on the glass fiber are smallerthan that for which 10 kpsi would cause failure. As such, the “size” ofa flaw in glass is often represented by stating the minimum tensilestress needed to cause catastrophic failure originating from that flaw.Thus, a glass fiber which has been stressed to 10 kpsi without breakingmay be said to have no flaws “larger” than 10 kpsi in strength. Whilethis representation of physical size by a stress with force units is abit of a misnomer, the characterization of flaw size in terms of stressis common in the art of glass strength. This is due to the simple factthat flaw depth is nearly impossible to measure directly and theindirect “strength” of the flaw is used as a surrogate.

As can be appreciated by the preceding discussion, the strength of glassis a consequence of the history of the glass. That is, newly-formedpristine glass is inherently exceptionally strong. As-formed glasssheets can approach the strength of newly-formed glass fibers, typicallyin excess of 700 MPa. However, subsequent handling or exposure toenvironmental factors can create flaws, or enlarge existing flaws,thereby weakening the glass. For this reason, newly drawn opticalfibers, for example, are immediately coated with a coating, such as apolymer coating, to protect the surface of the glass and prevent, or atleast minimize, a degradation in strength. As used herein, the term“as-drawn” or “as-formed” will hereinafter refer to a glass edge whichhas not been scored, cut, abraded, or otherwise processed after the edgehas been formed (that is, after the glass has cooled below its strainpoint and entered an elastic state where an applied load would deformthe glass elastically). Any edge processing (shaping, cutting and soforth) that occurs while the glass sheet or ribbon temperature is abovethe strain point during processing is considered “as-formed” exceptlocalized edge heating and re-flowing which may occurs when an edge isprocessed, such as with a CO2 laser. It should be understood that thisprocessing excludes routine contact with the glass, such as contactingthe glass during transportation, exposure to air, moisture, etc.

In the context of a downdraw process, the edges of the glass areconsidered as-formed as they descend through a temperature gradient andtransition from a viscous or viscous-elastic material to an elasticmaterial. In a conventional glass sheet making process, the as-formededges are removed after the glass cools below the strain pointtemperature, usually subsequent to the drawing process.

Shown in FIG. 2 is a glass ribbon 16 descending from a source (notshown). Glass ribbon 16 may be drawn by applying a force F to the bottomend of the ribbon. Alternatively, counter-rotating pairs of pullingrolls 18 at each edge of ribbon 16 may be used to draw the glass. Thesource may be a re-draw process, a single-sided overflow downdrawprocess, a two-sided fusion downdraw process or any other processwherein a viscous melt is drawn into a glass ribbon. In a conventionalglass sheet forming operation, glass sheet 20 is cut from ribbon 16along separation lines 21 and 22. As-drawn edge portions 24 and 26 areremoved, forming separation edges 28 and 30, usually subsequent to thedrawing process. Glass sheet 20 may then be used in a later display orelectronic device manufacturing process.

Economies of scale are typically realized in an electronic devicemanufacturing process by forming as many devices on a substrate sheet ascan be practically made to fit. Thus, as illustrated in FIG. 3, as manyelectronic device elements 32 (e.g. display elements 32) may be formedon glass sheet 20 as may fit. Device elements 32 may be, for example,one or more layers of an electrically active or inactive material, or anelectroluminescent material such as an organic light emitting diode(OLED) material. A device element may be, for example, one or morepixels of a larger display device, an electroluminescent material, etc.Glass sheet 20, comprising a plurality of electronic device elements 32is then further cut, such as along separation lines 34, to produceindividual electronic devices. For example, glass sheet 20 may comprisemultiple sets of device elements 32. Glass sheet 20 is then be separatedor subdivided such that each set of device elements 32 comprises anindividual display unit that may be incorporated into a more complexassembly, such as a computer monitor, television, cell phone, etc. Thefollowing description is directed primarily toward such display devices.However, it should be recognized that the following disclosure isapplicable to other electronic devices. As used herein, an electronicdevice is intended to denote any of a broad category of devices andassemblies including, but not limited to, display devices, photovoltaicdevices, radio frequency identification (RFID) devices, siliconsemi-conducting devices, organic semi-conducting devices and othergeneral electronic devices. On the other hand, an electronic deviceelement is intended to denote a singular component or set of componentsof any one of the foregoing devices or assemblies.

It should be readily apparent from the foregoing description that anindividual electronic device resulting from the above process includes aseparation edge on each side of the display. Generally, display devicesare rectangular in shape, and thus the display resulting from the aboveprocess would include four separation edges created subsequent to thedrawing process. That is, the entire perimeter of the display devicewould consist of separation edges, and likely include flaws of varyingsizes and tensile strengths. In the case of a flexible electronic devicewhich may be required to endure significant bending stresses, theprobability of failure due to fracture of the device is heightened bythe presence of the separation edges, since no matter what the directionof bending, a separation edge will be flexed or stressed. The presentinvention takes advantage of the high strength obtained from theas-formed edges of the ribbon, and a sheet cut from the ribbon.

As used herein, the general term “glass” is used to refer to thesubstrate material, but the substrate material is meant to include anyof a broad class of brittle inorganic materials comprising glasses,glass ceramics, and ceramics that can be formed from a viscous state.For example, a glass ceramic substrate can possess high strengthas-formed edges that are created when drawn from a viscous state beforeundergoing the crystallization step. Likewise, the substrate may becomprised of one or more inorganic layers at least one of whichpossesses as-formed edges. The substrate additionally may include aprotective polymeric or other layer along with the at least oneinorganic layer with as-formed edges.

In some embodiments of the present invention, the as-formed edges of theglass are contacted by pulling rolls that draw the glass downward, butthat deform the glass edges with which they are in contact at atemperature above the glass strain point. Indeed, in some embodimentsthe rolls may be used less for pulling and more for imparting a shape tothe ribbon edges, for example a taper, or a glass web extending from thesheet edge along the length of the ribbon, preferably down the center ofthe edge thickness (the neutral plane of the ribbon). Other methods ofshaping the as-drawn glass edges are also possible, such as with alaser, pressurized gas, or other methods.

In accordance with one embodiment, pulling rolls are not employed, andthe as-drawn edges of the drawn ribbon are not removed. Depicted in FIG.4 is a ribbon that may be formed much as that described relative to FIG.1, with the exception that the as-drawn edges are not removed. Glassribbon 38 may for example be rolled and stored for later use. In anyevent, glass ribbon 38 comprises a long dimension L (length L) generallyparallel to the as-drawn edges 40 and 42, and a width W transverse tothe length. Length L may vary with the particular process.

Width W of ribbon 38 is sized such that an electronic device element 32may be formed across the width of the ribbon. Thus, electronic deviceelements may be formed on glass ribbon 38 in a manner analogous to themanner in which images are sequentially formed on a strip ofphotographic film, such that ribbon 38 need only be separated along onedimension to form an individual electronic device, e.g. a displaydevice. The electronic device element or elements typically comprise atleast one layer of an electroluminescent, semi-conducting or conductingmaterial. For example, the device element may be an organic lightemitting material. Either before, or subsequent to, the formation of theone or more display or electronic device elements 32 on glass ribbon 38,individual display or electronic device substrates 44 are cut from theribbon along separation lines 46. For example, individual devicesubstrates 44 can be separated from glass ribbon 38 in a manner thatretains the as-formed edges 40 and 42 before a device element 32 isfabricated. Likewise, it is also possible to first fabricate a deviceelement 32 on the substrate 44 while it is still attached to theremaining glass ribbon 38. The first approach is suitable for batchprocessing of devices, and the second approach is suitable forcontinuous or roll-to-roll processing of devices. In both cases, theas-formed edges 40 and 42 of device substrate 44 are retained.

Specific examples described herein have dealt with display devices andflexible display devices in particular. Moreover, the high strengthsubstrate with as-formed edges can be used for several types of displaydevices such as organic light emitting, electrophoretic, liquid crystaland electro-wetting devices. In general, though, thin glass substrateswith high strength as-formed edges can be used for other electronicdevice applications outside of the display area. Such devices may becomprised of a single substrate with as-formed edges or multiplesubstrates with as-formed edges (top & bottom, backplane and colorfilter, backplane and encapsulating cover and so forth).

Likewise, although the term “flexible” is generally used to describe theglass substrate, the substrate need not be flexed either during thefinal application or during the device manufacturing process. The term“flexible” is used to point out that the substrate is thin enough andhas a high enough strength to survive bend radii less than about 30 cm,less than about 10 cm, less than about 5 cm, less than about 2 cm, orless than about 1 cm. For example, the final application for anelectronic device fabricated on a high strength substrate with as-formededges may require properties of thinness and light weight. Thisapplication would require a mechanically durable substrate, but bendingmay not occur in either the final use or a manufacturing processtherefor. Alternatively, a continuous or semi-continuous manufacturingprocess could be used to fabricate the electronic devices, thuspotentially requiring the substrate to experience a bend radius. In thiscase the final application may not require flexing of the substrate, buta cost effective manufacturing process could. A final example is withthe end application requiring the substrate to experience either a shortterm or long term bend radius. Devices may be manufactured for aflexible or conformable application in either a continuous or flat batchprocess.

When an individual display or other electronic device is cut from theribbon, the underlying glass sheet or substrate is generally rectangularin shape, with two sets of two opposing edges: a first pair of cut orseparation edges, and the second pair of un-cut, as-drawn edges. Theglass sheet has a thickness preferably less than or equal to 0.4 mm,preferably less than or equal to 100 μm. The as-formed edges can have atensile strength greater than about 500 MPa. On the other hand, thetensile strength of the separation edges is considerably weaker, in somecases less than about 200 MPa, the edge having been damaged during theseparation operation (e.g. by scoring and breaking). Thus, the strengthof the entire sheet is compromised by the low strength of the edges,i.e. the strength of the edges establishes the maximum strength of theentire sheet. One such resulting electronic device 44 is shown in FIG.5. Electronic device 44 comprises two as-formed edges 40 and 42, and twoseparation edges 48, 50 resulting from the separation from ribbon 38.Electronic device 44 may be a display device, or any other device asdisclosed herein.

Consider FIG. 6 showing glass substrate-based display or electronicdevice 44 comprising glass sheet 52 having separation edges 48, 50 andopposing as-drawn edges 40, 42 (display or electronic device element 32has been omitted from view for clarity) on glass sheet 52. Orthogonalaxes 60 and 62 are shown superimposed on the glass sheet such that axis60 is perpendicular to and intersects as-drawn edges 40 and 42, and axis62 that is perpendicular to and intersects separation edges 48 and 50.It should be apparent that axes 60 or 62 need not bisect theirrespective edges, nor is it necessary that they be perpendicular, eitherto themselves or to their respective edges. That is, bending is notnecessarily perpendicular to any one edge. However, the representationpresented here is illustrative.

If glass sheet 52 is bent in a manner that forms a generally “U” shapewith axis 60 running along the top of the U-shaped curve, separationedges 48, 50 are not bent, and experience no externally-applied tensilestress. On the other hand, as-formed edges 40 and 42 are bent. Becauseedges 40 and 42 are the as-formed edges and possess high strength, thesheet is less likely to fracture. If, however, the sheet 52 is insteadbent orthogonal to axis 60 such that axis 62 runs along the top of theU-shaped curve as shown in FIG. 7, separation edges 48, 50 are subjectedto stress—compression stress at surface 64 and tensile stress at surface66. If the bend is sufficiently tight (having a small bend radius), andthe flaws produced at edges 48, 50 by the separation/cutting process areof a strength lower than the applied tensile stress, the sheet canfracture.

There are many applications contemplated for flexible displays orelectronic devices where just such bending may be experienced. Forexample, the flexible display or electronic device may be in the form ofa roll or coil that is uncoiled for viewing, then re-coiled for storage.If the flaw-prone separation edges of the device are parallel with theaxis of the coil, the separation edges will experience minimal stress.Stresses resulting from the bending are instead borne by thehigh-strength as-formed edges. Additionally the device may be bent onceduring installation and held at that bend radius continuously throughoutits lifetime. This also requires a high strength continuously bent edgedue to the well-known phenomenon of glass fatigue. Continuous,semi-continuous, or batch manufacturing processes may also require largetensile or other strength requirements along the as-formed edges.

Shown in FIG. 8 is another embodiment of the present invention wherein atapered shape has been imparted to the as-formed edges of a glassribbon, such as by paired rolls 68. As shown, the extreme edge of glassribbon 70 is substantially thinner than the remainder of the ribbon. Forexample, the edge may comprise a thin ridge 72 of glass that extendsfrom the body of the ribbon midway between the front and back surfaces74, 76 respectively, of the ribbon and extending along the length of theribbon.

As a glass object, such as glass sheet 52 is bent, two stress zones areformed—a compression zone C and a tensile zone T. As shown in FIG. 9,the tensile zone forms at the outside of the bend, whereas thecompression zone forms at the inside of the bend. As one moves from theoutside to the inside, the tensile stress in the tensile stress zonegradually decreases, passes through zero, and becomes a compressivestress. That is, as one moves through the thickness of the glass sheet,the stress transitions from tensile to compressive, or compressive totensile. The stress midway between the two surfaces is zero, and may bereferred to as the neutral plane N. Glass fails under stress (tensile),and if the ridge region described supra is formed along the neutralplane of the sheet, flaws existing at the ridge are less likely to serveas the source of failure because the stress is minimal at this location.

Shown in FIG. 10 is a cross sectional view of an exemplary electronicdevice 80, e.g. a display device, in accordance with an embodiment ofthe present invention comprising glass sheet 82 separated from ribbon70. The as-formed edges are shown to the right and left hand side ofFIG. 10, whereas the separation edges are into and out of the page. Anelectronic device element 32, such as an electroluminescent,semi-conducting, or conducting material (e.g. organic light emittingmaterial, silicon (Si), or indium tin oxide (ITO) coating) is disposedover glass sheet 82. Device 80 may also include one or more barrierlayers 84 that provides a hermetic seal with glass sheet 82 and thus ahermetic package for device element 32. The barrier layer may be formedovertop of electronic device element 32 or beneath device element 32(between glass sheet 82 and device element 32) or disposed oppositeglass sheet 82 from device element 32. Barrier layer 84 may be, forexample, a glass layer, a polymer layer or any other material capable ofproviding hermeticity. Glass sheet 82 is shown comprising edge ridges 72disposed along neutral plane N of glass sheet 82. Ridges 72 may beformed, for example, by rollers during any of the previously describeddowndraw processes, as illustrated in FIG. 8. As should be apparent fromthe preceding example (i.e. FIG. 9), bending display 80 (e.g. glasssheet 82) such that ridges 72 are non-planar, for example, in a “U”shaped bend as illustrated in FIG. 9, the ridges experience littlestress, being located along the neutral plane of the glass sheet. Thus,even if damaged, the as-drawn edges comprising ridges 72 are unlikely toprecipitate a fracture.

To illustrate an embodiment of the invention, a Corning code 1737G glasssheet was cut to appropriate dimensions as a preform in a redrawprocess. The preform was redrawn and the resultant glass ribbon was cutinto 40 mm lengths while preserving the as-drawn edges. The 40 mm longsamples were bent into a “U” shape between two moving parallel plates totest the two-point bend strength of the as-formed edges. Two point bendtesting is a common method of testing the strength of glass articles,including glass fibers. A sample is plated between two fixtures in a “U”shape and one or both of the fixtures moved together. The size of theglass article and the distance between the fixtures (e.g. the bendradius of the article) can be used to determine the tensile stressexperienced by the article at failure. See, for example,Telecommunications Industry Association Bulletin no. TSB62-13. Theplates were moved together at a closure rate of 0.1 mm/s until thesample failed (broke). The results of that test are shown in FIG. 11.FIG. 11 depicts data points for the minimum bend radius achieved foreach sample as a function of the sample thickness. The 1737G samples(86) were able to achieve a minimum bend radius of less than 30 mm inmany cases, and in some cases, less than 20 mm, and in other cases lessthan 10 mm. The same test was also performed on Corning 0211 Microsheetglass sized by laser cutting and plotted on in FIG. 11 (88). FIG. 11shows that even though the 0211 Microsheet samples were thinner than theredrawn 1737G sample, many of the 1737G samples were able to achieve amuch smaller bend radius before failure than the 0211 Microsheet sample.The minimum achievable bend radius before failure for the 0211Microsheet samples was 30 mm.

In another experiment, Corning Eagle2000F™ glass sheets were cut to sizeand redrawn to glass sheets having dimensions of approximately 0.4 mmwide by 40 μm thick by 50 cm long. The redrawn samples were thenstrength tested in tension to failure at a rate of approximately 180MPa/s in air. The median recorded strength was approximately 1000 MPa.

While the invention has been described in conjunction with specificexemplary embodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart in light of the foregoing description. Accordingly, the presentinvention is intended to embrace all such alternatives, modifications,and variations as fall within the spirit and broad scope of the appendedclaims.

1. A method of making an electronic device comprising; providing aribbon of inorganic material having opposing as-formed edges along alength of the ribbon; forming an electronic element on the ribbon; andseparating the ribbon to form a sheet of inorganic material havingopposed as-formed edges and an electronic element disposed thereon. 2.The method according to claim 1 wherein a minimum tensile strength ofthe inorganic sheet is greater than about 500 MPa.
 3. The methodaccording to claim 1 further comprising coating the as-formed edges ofthe ribbon with a polymer.
 4. The method according to claim 1 whereinthe ribbon of inorganic material comprises a glass, a glass ceramic or aceramic.
 5. The method according to claim 1 wherein the as-formed edgesof the sheet of inorganic material comprise a ridge disposed proximate aneutral plane of the sheet.
 6. The method according to claim 1 whereinthe electronic element comprises at least one layer of anelectroluminescent, semi-conducting, or conducting material.
 7. Themethod according to claim 6 wherein the at least one layer ofelectroluminescent material is an organic material.
 8. An electronicdevice comprising: a sheet of inorganic material comprising a thicknessless than about 0.4 mm and at least two as-formed edges; and at leastone layer of an electroluminescent, semi-conducting, or conductingmaterial disposed over the inorganic sheet.
 9. The electronic deviceaccording to claim 8 wherein the sheet of inorganic material comprises aglass, a glass ceramic or a ceramic material.
 10. The electronic deviceaccording to claim 8 wherein a minimum tensile strength of the sheet ofinorganic material is at least about 500 MPa.
 11. The electronic deviceaccording to claim 8 wherein the thickness of the sheet of inorganicmaterial is less than about 200 μm.
 12. The electronic device accordingto claim 8 wherein the sheet of inorganic material is coated with apolymer.
 13. The electronic device according to claim 8 wherein aminimum bend radius before fracture of the sheet of inorganic materialin a two-point bending test at a closure rate of 0.1 mm/s is less than30 mm.
 14. The electronic device according to claim 8 wherein theelectroluminescent, semi-conducting, or conducting material is anorganic material.
 15. An electronic device comprising: a substratecomprising a glass sheet formed by a downdraw process, the glass sheethaving a thickness less than about 0.4 mm and at least two as-formededges in an opposed relationship; and an electrically active materialdisposed over the glass sheet.
 16. The electronic device according toclaim 15 wherein the thickness is less than about 0.2 mm.
 17. Theelectronic device according to claim 15 wherein a tensile strength ofthe glass sheet along the as-formed edges is greater than about 500 MPa.18. The electronic device according to claim 15 wherein the electronicdevice is an electroluminescent display device, a liquid crystal displaydevice, an electrophoretic display device, or an electro-wetting displaydevice.
 19. The electronic device according to claim 15 wherein theelectronic device is a photovoltaic device, a radio frequencyidentification device, or a lighting device.
 20. The electronic deviceaccording to claim 15 wherein the substrate comprises a plurality oflayers, at least one of the layers having at least two as-formed edges.